Two beaches with significant differences in grain size and thus in
beach profile morphology and response to wave conditions were studied on
the Oregon coast. Gleneden Beach, just south of Siletz Spit and Lincoln
City, has a median grain size of 0.36 mm (medium sand) and a steep beach
face slope, while Devil's Punchbowl Beach has a median grain size of
0.23 mm (fine sand) and low concave-up beach face slope.
Eleven beach profile surveys were obtained at Gleneden Beach and
twelve at Devil's Punchbowl Beach between August 1976 and April 1977; on
average once every two weeks during spring tides. Gleneden Beach showed
the typical change from a swell profile with a wide berm that prevails
during summer months to a storm profile with little or no berm that
exists during the stormy winter months. This transition occurred in
August and September, being completed by early November. The finer-grained
Devil's Punchbowl Beach also showed general erosion during the
fall. However, a transition from a swell profile to a storm profile is
not as clear there as the beach has little berm, even in mid-summer, and
always has a concave-up appearance typical of the winter storm profile.
Gleneden Beach and Devil's Punchbowl Beach did not always agree in
their responses to the changing wave conditions. One may be eroding at
the same time the other is accreting. These differences in response to
changing wave conditions appear to result from their differences in
grain size.
Volume changes of the erosion or deposition at the two beaches
were computed from successive beach profiles. The coarser-grained
Gleneden Beach showed larger changes in erosion and deposition, the
maximum erosion being 0.71 m³ per meter of profile length, while the
finer-grained Devil's Punchbowl Beach showed a maximum erosion of 0.25 m³
per meter of profile length. Attempts were made at relating the erosion
or deposition and the volumes of erosion/deposition to the wave breaker
heights and deep-water wave steepness that occurred between the beach
profile sequences. There is only a vague relationship between the volumes
of beach erosion/deposition and the wave heights, the probability
of erosion increasing and the volume of sand eroded increasing with increasing
wave breaker heights. The maximum wave heights that occur
during the time interval appear to be most important to the volume of
erosion, erosion volumes being large if storm breaker heights reach 5
to 6 meters or greater. Deposition prevails when the average breaker
heights fall below 4 meters and storms are limited to breaker heights
less than 5 meters. The deep-water wave steepness shows little relationship
to the erosion or deposition volumes, indicating that the wave
period is not as important a parameter as the wave height to beach erosion. / Graduation date: 1977
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28554 |
| Date | 09 May 1977 |
| Creators | Aguilar Tunon, Nicolas A. |
| Contributors | Komar, Paul D. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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